The present application is based on Japanese Priority Document 2000-215692 filed on Jul. 17, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a wire dot printer and a wire dot printer using the same.
2. Discussion of the Background
There is already provided in the related art a wire dot printer head in which a plurality of cores and yokes arranged in an annular shape are integrally formed by magnetic material, a coil is fitted to each of these cores, a plurality of armatures having wires fixed at their extremity ends with means such as a brazing and the like are arranged in a radial form, and supported so as to be raised or lowered in respect to the cores, and the extremity ends of the wires are arranged in rows by the extremity end guides to be slidably supported. Such a wire dot printer head as above is moved in a main scanning direction in parallel with the platen while being mounted on a carrier, the specified coil is excited during its moving process to drive the armature and then the extremity ends of the wires are struck against the printing medium on the platen to perform a printing operation.
In turn, when the extremity ends of the wires are arranged in rows by the extremity end guide on a straight line extending along a sub-scanning direction crossing at a right angle with a main scanning direction acting as a moving direction of the wire dot printer head, for example, if an alpha-numerical letter of xe2x80x9cIxe2x80x9d is printed, the wires arranged in the sub-scanning direction must be driven at once. With such an arrangement as above, some problems, for instance, that the capacity of power supply is increased and noise generated when the wires strike against the platen is increased, occur.
In view of this fact, as already described in the gazette of Japanese Patent Laid-Open No.Sho 54-24115, there is provided a proposal in which the extremity ends of the wires are arranged in two rows along the sub-scanning direction, the extremity ends of the wires are arranged in a zig-zag form in such a way that the arrangement positions in the sub-scanning direction of the wires in the first row and the wires in the second row are displaced only by a pitch corresponding to a half of a diameter of wire, and even in the case where the letter of xe2x80x9cIxe2x80x9d is to be printed, all the wires in the first row are driven, thereafter the wire dot printer head is moved in the main scanning direction only by a space between the wire in the first row and the wire in the second row, and then all the wires in the second row are driven, whereby one character is printed in twice operations.
In addition, as already described in the gazette of Japanese Patent No.2958010, the extremity ends of the wires are arranged on the two arcs or arranged along a contour of rhomb.
However, when the extremity ends of the wires are arranged on the arc or the contour of rhomb, it may provide an effect that the number of wires driven at once can be reduced. However, the number of drivers driving the wires under a different timing is increased and control over the application of voltage becomes complicated.
In view of this fact, it is yet desired to provide a configuration in which the extremity ends of the wires are arranged on a straight line along the sub-scanning direction. Also in the case where the extremity ends of the wires are arranged on the straight line, the configuration in which the wires are classified in two rows and arranged in a zig-zag form can perform a printing by driving the entire wires in separate two segments and then the capacitance of the power supply and noise can be reduced to a certain degree. This configuration is sometimes employed in a specific less-expensive product because the number of drivers can be sufficiently less and a control is not so complicated as compared with the configuration in which the extremity ends of the wires are arranged on an arc and on a contour of rhomb.
As described above, in the case of the wire dot printer head having the structure in which the extremity ends of the wires are arranged on the straight line along the sub-scanning direction, the armatures are oppositely faced against the cores arranged in an annular form, thereby the rear ends of the wires are arranged in an annular form and the extremity ends are arranged on the straight line, so that the wires are bent little by little by a plurality of guides as the wires are faced from the rear ends toward the extremity ends. As the plurality of guides, it is needed to provide an intermediate guide for forcedly bending the intermediate part of the wires and the extremity end guides which arranges the extremity ends of the wire on the straight line. In addition, it is also carried out that either one vibration-proof guide or a plurality of vibration-proof guides for preventing wires to contact each other when an impact is applied are arranged between the intermediate guide and the armatures.
Referring to FIGS. 9 to 13, this example will be described as follows. FIG. 9 is an illustration for showing the arrangement pattern of the extremity ends of the wires. This arrangement is attained by the extremity end guide and the number of wires is 24 (called as 24-pin), although the extremity ends of the wires 9 are classified into two rows in parallel with the sub-scanning direction (the direction of arrow Y) and arranged on the straight line in the same manner as that described in the gazette of Japanese Patent Laid-Open No.Sho 54-24115. In FIG. 9, as the wires 9 in the left row, the wires 9 in odd number from upper 1 (#1) to 23 (#23) are arranged and as the wires in the right row, the wires 9 in even number from upper 2 (#2) to 24 (#24). The arrangement positions of the wires 9 arranged in two rows in the sub-scanning direction are displaced only by a xc2xd of an arrangement pitch (p) in the sub-scanning direction of the wires 9 in every row. A row space of the wires 9 divided in two rows is {fraction (1/20)} inch at a center distance.
FIG. 10 is an illustration for showing the coordinate positions at a plurality of locations in the same plane ranging from the rear ends to the extremity ends of the wires in respect to the center of the wire dot printer head. The plurality of locations correspond to the rear ends of the wires (portions brazed to the armatures) indicated by xe2x96xa1 mark; the portions supported by the first vibration-proof guides indicated by + mark; the portions supported by the second vibration-proof guides indicated by ⋄ mark; the portions supported by the intermediate guide indicated by x mark; and the portions supported by the extremity end guides indicated by the ◯ mark, respectively.
FIG. 11 is an illustration for showing a distance ranging from the rear ends (xe2x96xa1) to the extremity ends (◯) of the wires on the same plane including the extremity end surfaces of the wires. As shown in FIG. 11, it is apparent that a distance L indicated by a straight line ranging from the rear ends (xe2x96xa1) to the extremity ends (◯) of the wires is short as the wires are directed to the upper part and the lower part of the row, and long as the wires are arranged near the center of the row. The length of this distance L is proportional to a wire bending amount and a bending stress.
In the case where the first and second vibration-proof guides are members for restricting the wires to contact each other when impact is applied, the wires do not accept any pressure from the first and second vibration-proof guides under their standstill state. However, the they are bent by the intermediate guide and the extremity end guide, and the wires arranged near the center of the row and having large amount of bending receives higher load from the extremity end guide and the intermediate guide. FIG. 12 is a graph in which a relation between the wire arrangement positions and a load accepted by the wires from the extremity end guide and the intermediate guide is attained by experiment. Numerical values indicated at an abscissa denote wire arrangement positions (No. 1 to No. 24) and numerical values indicated at an ordinate denote a sum of a lad that the wires accept from the extremity end guide and the intermediate guide.
FIG. 13 is a graph in which a relation between the wire arrangement positions and a wire bending is attained by experiment. Numerical values indicated at an abscissa denote wire arrangement positions (No. 1 to No. 24) and numerical values indicated at an ordinate denote a wire bending stress. In this graph,
{circle around (1)} indicates a wire bending stress under a non-printing state:
{circle around (2)} indicates a wire bending stress when the wires strike against the platen: and
{circle around (3)} indicates a sum of stresses {circle around (1)} and {circle around (2)}.
As apparent from the foregoing description, if the wire extremity ends are arranged on the straight line along the sub-scanning direction, the wires arranged near the center of the row, when the wire is seen from the extremity ends, may accept a large bending amount, a large bending stress and a large load accepted from the extremity end guide and the intermediate guide and their sliding characteristic is deteriorated. As a result, there occurs a problem that the brazed part at the rear end is peeled off at the armatures due to repetition of printing operation.
Accordingly, an object of the present invention is to reduce a wire bending stress and improve durability without making any complex control over the printing operation.
The object of the present invention is achieved by the novel dot printer head and dot printer using the same of the present invention.
According to the novel dot printer head of the present invention, a plurality of wires driven by the armatures displaced under electrical excitation to the coils to apply an impact force for printing operation are supported by the extremity end guide. The extremity end guide has a plurality of guide holes for independently and slidably supporting the extremity ends of the wires and arranging them in rows. The guide holes at the extremity end guide form one or more groups, and the extremity end guide holes in each of the groups are set such that the wires are classified into a plurality of sub-groups with a plurality of wires where the rear ends of wires are adjacent to each other within a specified range being classified as one sub-group, the extremity ends of the wires are arranged on a straight line in a sub-scanning direction in a unit of each of the sub-groups, and the arrangement positions of the extremity ends of the wires in the main scanning direction are made different in response to a difference in the arrangement positions of the rear ends of the wires for every different sub-groups such that the bending stress of the corresponding wires may become low as compared with the case where the extremity ends of all the wires are arranged on a straight line.
Another aspect of the present invention relates to a wire dot printer using the wire dot printer head of the present invention. According to the novel dot printer of the present invention, a sheet transferring passage for guiding a sheet, transfer rollers for transferring the sheet in the sheet transferring passage, a platen arranged along the sheet transferring passage and a wire dot printer head of the present invention are provided, wherein voltage is applied to the coil for driving respective wires in response to the arrangement positions of the wire extremity ends in the main scanning direction while changing its timing.